Applications such as semiconductor fabrication processing increasingly require more accurate measurements, lower equipment costs, and quicker and more consistency in timing in the delivery of gases from components such as a mass flow controller (MFC).
An MFC is a device used to measure and control the flow of fluids and gasses. Conventionally, in pressure based MFC, a pressure transducer is needed within an MFC to measure the process gas pressure in a known volume and temperature.
FIG. 1A is a schematic diagram illustrating a prior art pressure based MFC 100 with a volume (V1) in conduit 198A that is used to measure pressure, according to a prior art embodiment. MFC 100 has an inlet port 101, an outlet port 102, a proportional inlet valve 103, a first pressure transducer 104, a restrictor 105, a second pressure transducer 106A and a temperature sensor 107. The first pressure transducer 101 measures pressure over V1 as an input for pressure regulation and is operates so that pressure at the first pressure transducer 104 closely matches the pressure at an inlet of the restrictor 105. The second pressure transducer 106 is located downstream and a temperature sensor 107A is used to increase accuracy.
FIG. 1B is a block diagram of FIG. 1A illustrating a flow order for a process gas through the prior art pressure based MFC 100B, according to an embodiment of a prior art embodiment. As shown, a process gas moves through a proportional valve 103B to a conduit containing V1 199B where the process gas is measured by a first pressure transducer 104B. Next the gas passes through restrictor 105B into a conduit with volume V2, 199B, where the pressure representative of the pressure at the outlet of the restrictor is measured. Finally, the process gas often exhausts from the MFC 100B to a process through an isolation valve actuator and seat 110.
Problematically, the space consumed by V1 hinders further efficiencies in accuracy, bleed down performance, space consumption and costs of gas delivery systems used for processing. Furthermore, when an external control directs the MFC to stop or reduce the magnitude of the gas flow to a lower rate of flow, V1 produces undesirable slow bleed down times to the new flow value.
What is needed is a flow node to provide an accurate delivery of process gas without the inefficiencies of a conventional MFC having an local pressure measurement directly on V1, by utilizing a remote pressure measurement of V1 pressure to reduce the bleed down volume while still providing pressure measurements that represent the pressure of the gas inlet to the restrictor with sufficient accuracy to maintain the specified accuracy of the flow device.